Unlike conventional optical elements that use refraction and reflection, diffractive optical elements (DOEs) directly control an optical phase using an optical diffraction phenomenon that occurs at a minute bumpy structure of a surface. DOEs are optical elements that can achieve miniaturization of electronic components or devices which has been increasingly demanded in recent years. Such DOEs are manufactured by dry etching that provides micromachining with high precision.
Dry etching is performed as follows. First, an insulative substrate composed of ZnSe or the like that is a material of optical elements is placed in a chamber. A secondary product is formed through a chemical reaction between the insulative substrate and an activated species in plasma generated when high-frequency power is applied to the insulative substrate. Positive ions also generated in the plasma are made to collide with the secondary product to remove the secondary product. Thus, dry etching is performed.
However, conventional dry etching has a problem in that, when positive ions collide with an insulative substrate or a chemical reaction occurs, the temperature of the insulative substrate is increased and thus the etching rate (speed) is not stabilized. The variation in etching rate leads to the variation in etching depth of the insulative substrate. Consequently, desired performances of DOEs cannot be achieved.
To solve the problem, a dry etching method is proposed in Patent Document 1. In the method, the etching rate is stabilized by attaching an insulative substrate to a conductor through conductive grease, which suppresses the variation in the etching rate between insulative substrates when a plurality of insulative substrates is simultaneously dry-etched.
Citation List
Patent Document
Patent Document 1: JP2005-157344A